1921 Persian coup d''etat (Persian: کودتای ۳ اسفند ۱۲۹۹) refers to several major events in Iran (Persia) in 1921, which eventually led to the establishment of the Pahlavi dynasty as the ruling house of the country in 1925. The events began with a coup led by Reza Khan, supported by Persian Cossack Brigade on February 1921. With this coup Reza Khan established himself as the most powerful person in Iran. The coup was largely bloodless and faced little resistance. With his expanded forces and the Cossack Brigade, Reza Khan launched successful military actions to eliminate separatist and dissident movements in Tabriz, Mashhad and the Janglis in Gilan. The campaign on Simko and the Kurds turned less successful and spanned well into 1922, though eventually concluding with Persian success.

In late 1920, the Persian Soviet Socialist Republic in Rasht was preparing to march on Tehran with "a guerrilla force of 1,500 Jangalis, Kurds, Armenians, and Azerbaijanis", reinforced by the Bolsheviks'' Red Army. This fact, along with various other disorders, mutinies and unrest in the country created "an acute political crisis in the capital."

By 1921, the ruling Qajar dynasty of Iran (at that time also known as Persia) had become corrupt and inefficient. The oil-rich nation was somewhat reliant on the nations of Britain and Russia for military and economic support. Civil wars earlier in the decade had threatened the government, and the only regular military force at the time was the Cossack Brigade.

The Qajar shah in 1921 was Ahmad, who had been crowned at the age of eleven. He was considered to be a weak, incompetent ruler, especially after British, Russian, and Ottoman occupations of Iran during World War I. In 1911, when the capital city, Teheran had been seized by the Russians, armed Bakhtiaris tribemen, rather than Iranian regular troops, expelled the invaders. This further diminished the government''s reputation, rendering it almost powerless in time of war.

Britain, which played a major role in Iran, was dismayed by the Qajar government''s inability to rule efficiently. Because of the inefficiency, Britain was locked in a power struggle with Russia, each nation hoping to control Iran.

In early 1921, an officer in the Qajar Cossack Brigade, Rezā Khān (became Reza Shah), decided to support a planned coup, the plotters of which hoped to install a more capable government. The British cast their lot in favor of Pahlavi.

The coup and subsequent events Pahlavi seizes Tehran

On February 18, 1921, Reza Khan and his Cossacks reached Teheran meeting little resistance. On early morning of February 21, they entered the city. Only several policemen, taken by surprise, are said to had been killed or wounded in the center of Teheran. Backed by his troops, Khan forced the government to dissolve and oversaw his own appointment as minister of war. Khan also ensured that Ahmad, still ruling as shah, appointed as prime minister Sayyed Ziaoddin Tabatabaee.

Treaty with the USSR

On February 26, the new government signed a treaty of friendship with the Union of Soviet Socialist Republics, formerly the Russian Empire. As a result of the treaty, the Soviet Union gave up some of its former Russian facilities in Iran, although the Soviet diplomats ensured that their nation was allowed to intervene with its military in Iran, as long as the intervention was "self defense." The USSR also gave up any Russian-owned railroads and ports in Iran.

Change of prime ministers

Prior to the coup, Ahmad Qavam, governor of Khorasan, had asserted his loyalty to the Qajar regime. When he refused to recognize the government, installed by Pahlavi, he was jailed in Teheran. During his imprisonment, Gavam nurtured a hatred of the man who had arrested him, the gendermerie chief Pesyan.

Sayyed Ziaoddin Tabatabaee, who had been installed as prime minister, was removed from office on May 25, by Shah Ahmad''s decree. Shortly afterward, Qavam was released from prison and given Tabatabaee''s former post.

Quelling local uprisings Pesian''s revolt

After Gavam was made prime minister, the gendermerie chief Pesyan found himself in dire straits and departed Teheran. Soon at the head of a rebel army, Pesyan went to battle with the armies of several regional governors. However, the rebels were eventually defeated and Pesyan was killed. The Kurds of Khorasan also revolted in the same year.

Gilan campaign

The campaign on the Republic of Gilan was taken in early July 1921, by the main Cossack force, led by Starosselsky. Following a gendarme operation, led by Habibollah Khan (Shiabani), they cleared up Mazandaran and moved into Gilan. On August 20, ahead of the arrival of the Cossacks, the insurgents pulled out of Rasht, retreating towards Enzeli. The Cossacks entered Rusht on August 24. Though further pursuit after the revolutionaries turned successful at Khomam and Pirbazar, they have become heavily assaulted later on by the Soviet fleet, which bombed them by heavy artillery fire. First, it had been believed that the entire force of 700 men, led by Reza Khan, became annihilited in this event, though later the actual casualty rate cleared to be about 10%, with the rest of them scattering upon the bombardment. As a result, Starosselski ordered evacuation of Rasht.

The Soviet Republic of Gilan officially came to an end in September 1921. Mirza and his German friend Gauook (Hooshang) were left alone in the Khalkhal Mountains, and died of frostbite.

In the aftermath of 1921 events, relations of Persian government with the Sheikhdom of Mohammerah had also become strained. In 1924, Sheikh Khazal rebellion broke out in Khuzestan, being the first modern Arab nationalist uprising led by the Sheikh of Mohammerah Khaz''al al-Ka''bi. The rebellion was quickly and effectively suppressed with minimal casualties.

Reza Khan took the throne for himself in 1926, taking the surname Pahlavi and thus founding the Pahlavi dynasty. The Pahlavis ruled in Iran until the revolution of 1979, when the government was toppled and replaced with that of the Islamic Republic of Iran, headed by Ruhollah Khomeini.